1. Field of the Invention
Exemplary embodiments of the present invention relate to a microprocessor, and particularly, to a technology for coping with external attacks through a debugging interface in a system based on an ARM core.
2. Description of Related Art
A microprocessor system based on an ARM core has been widely used in various technological products, for example, storage devices such as a smart phone, a tablet PC, a hard disk drive (HDD), or the like, various communication devices, a wireless mouse, home appliances, electronic devices, various types of sensors, etc.
A joint test action group (JTAG) has generally been used in order to develop and verify products based on the ARM core. That is, in many systems in which microprocessors are used, the development and verification of products have been conducted by using the JTAG as a debug port for debugging.
In the processor based on the ARM core, an external debug request signal (EDBGRQ) generates a halting debug event, which causes a processor to enter into a debugging state.
External signals, such as JTAG, EDBGRQ, and the like, can threaten security by taking control of the processor, accessing a register or a memory, or the like. That is, attempts to obtain important information or modulate data by accessing a system using JTAG have been frequently conducted.
Therefore, systems that use the signals have security vulnerability. Therefore, various attempts have been made to solve the problem.
U.S. Pat. No. 7,117,352 discloses a method for inactivating a debug port for a JTAG debugging interface by providing one-time-programmable (OTP) memory and using an internal ROM. However, the method increases manufacturing costs due to the use of the OTP, and the JTAG cannot be used again once the JTAG has been inactivated using the OTP register.
That is, JTAG is currently recognized as essential to industry, and is widely used, but three interests, namely security, economics, and utilization, have been considered as important issues. Therefore, a new technology for simply and assuredly improving security for a JTAG is urgently needed.